Class AbstractSearchFilterVisitor

SearchFilterVisitor is a base class used to optimize finding specific information
in the filter data structure.

This differs slightly form the DefaultFilterVisitor case in that you can abandon the depth
first traversal at any point by returning true from found( object ).

Most implementations accept the default functionality which simply checks if data is non null.
This allows you to simply return an object from any method the moment you have found what
you are looking for.

visitNullFilter

This is particularly used during data structure transofrmations, however
the use of null is not recommended. Please make use of Filter.NONE
and Filter.ALL as placeholder objects that communicate intent.